1 Field of the Invention
The invention relates to discharge lamp ballasts, lighting systems and projectors that apply starting voltage across discharge lamps at a starting mode and supply the lamps with DC power for steady operating (lighting) at a steady operating mode after the starting mode.
2 Description of the Related Art
A discharge lamp ballast for a DC discharge lamp comprises a voltage step down converter in order to supply the lamp with DC power for a steady operating state at a steady operating mode. Also, in case that the lamp is a high pressure discharge lamp (HID lamp) such as a metal halide lamp or the like, the ballast is provided with an igniter that generates high voltage pulse from several kV to 10 s kV with a pulse transformer (see, e.g., Japanese Patent Publication number H10-144488).
However, when the above transformer provides the lamp with high voltage from several kV to 10 s kV, electromagnetic induction noise (flux) is radiated from the transformer and therefore there is a problem that the noise gives the ballast and peripheral circuits erroneous operation.